BMP testingBy-products of the agri-food industry

Oil refining residues (gums, condensates, spent earth) — BMP: 5 studies, weighted mean 714 m³ CH₄/t VS

Oil refining residues (gums, condensates, bleaching earth) are concentrates of fats and lipids with a high gas potential and LCFA risk.

CH₄ ≈ 63 % (estimate)

Published 9 April 2025Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Khalid Mahmood / Wikimedia Commons, licence CC BY-SA 3.0, source file; changes: cropping

Weighted mean: 714m³ CH₄/t VS
Range: 426–866m³ CH₄/t VS
Records: 5studies
Publications: 2sources
Temperatures: 35 °C, 38 °Cof the test

Methane in biogas

≈59–68% CH₄

High methane content · ≈ 6.3 kWh/m³ of biogas

estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (carbohydrate-dominated (no protein or fat characteristics); fat-rich (process classification)) and the yields of compound groups according to FNR.

How we calculate it and what the zones mean

Rating for biogas plants

not rated — editorial rating for biogas plants

Not rated: no dry matter or volatile solids in the data. We calculate the rating when the dry matter and volatile solids of the material are known.

Editorial rating per the methodology

Add to the co-digestion calculator CSV data

BMP curves from 5 studies

Weighted mean Individual records

Dashed lines are a model curve (first-order kinetics, B(t) = B₀·(1 − e^−kt)); the end point comes from the publication. All curves are model curves.

Cumulative methane production over the test [m³ CH₄/t VS]. The thick line is the weighted mean of all records (714); dots mark the end values given in the publications. Point at the chart to read values; click a legend item to hide or show a record.

Records and sources

Download CSV

Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Dubrovskis i Plume (2024) DOI	814	38 °C · mesophilic	Rapeseed oil refining by-product	end point (model curve)
Kouas et al. (2017) · 1 DOI	426	35 °C · mesophilic	condensate (sunflower oil)	end point (model curve)
Kouas et al. (2017) · 2 DOI	504	35 °C · mesophilic	condensate (palm oil)	end point (model curve)
Kouas et al. (2017) · 3 DOI	664	35 °C · mesophilic	oil	end point (model curve)
Kouas et al. (2017) · 4 DOI	866	35 °C · mesophilic	gum	end point (model curve)
Weighted mean	714	arithmetic mean 655, SD 190

Process properties

fat-rich
tendency to foam
forms a floating layer
low in nitrogen
variable composition
editorial classification

Low confidence: the description is based on general characteristics of the substrate group, not on studies of this material. Treat it as a hint to be verified.

Advantages

Methane potential in the Substraty.pl BMP dataset: weighted mean 714.5 m³ CH₄/t VS (SD 190.5; 5 records, 2 sources).
A lipid concentrate of high potential (Long et al. 2012).

Drawbacks and risks

Free LCFA inhibit methanogenesis and cause flotation (Long et al. 2012; Elsamadony et al. 2021).
Low N content requires a slurry base.

Co-digestion — what to combine it with, what to watch out for

combines well
substrates: high alkalinity (buffer) — e.g. Cattle manure, Pig slurry, Cattle slurry, Duck slurry, Rumen and digestive tract content
Slurry supplies N and alkalinity, balancing the high C/N of the material.^[1][2]
avoid
substrates: fat-rich — e.g. Food waste, Spent coffee grounds, Primary sludge, Sunflower seeds, Olive pomace / olive mill solid waste
^[3]

Dosing

No source-based threshold; apply the shared lipid limit, start low.

Introduce gradually, starting with a small dose and monitoring the process (e.g. FOS/TAC, pH, gas composition).

Sources of the process data

The co-digestion calculator will assess a specific mixture containing this substrate.

What it is and where it comes from

The refining of vegetable oils consists in removing impurities and undesirable components from crude oil. The successive stages generate wastes: gums (degumming, rich in phospholipids), deodorisation condensates (free fatty acids and volatile compounds), and spent bleaching and filtration earth, on which oil is deposited. In Poland rapeseed and sunflower oil refineries are significant, and the materials described here include sunflower and palm oil condensates and earth from the winterisation of sunflower oil.

Properties relevant to digestion

The main components are lipids in various forms: phospholipids in gums, free fatty acids in condensates, and oil adsorbed in earth. Such wastes have a very high energy potential, because fats give more methane per unit of dry matter than carbohydrates. At the same time free long-chain fatty acids are inhibitors of methanogenesis and cause foaming and flotation of biomass. Bleaching earth additionally contains mineral components which do not ferment. The low nitrogen content requires combining with slurry or protein-rich material.

How to read the spread of results

The dataset contains several records from a small number of sources, mainly one study, so independent verification is limited. They describe different materials: condensates, earth and gums, which have different compositions, so the variability stems more from the type of waste than from measurement error. The result is also affected by the type of oil (sunflower, palm, rapeseed), the degree of refining, the share of adsorbed fat in the earth, size reduction, the inoculum and the adaptation of the microflora to lipids.

In biogas plant practice

Refining wastes are used at a limited share, dosed gradually and evenly to avoid lipid shock. Combining with slurry and constant monitoring of volatile acids and gas production are recommended. Fatty materials may require heating for pumping. Waste from the food industry is waste, so its acceptance requires appropriate authorisations. Spent earth has limited use because of its mineral content.

It should be noted that the internal diversity of this group is so great that an average for it has limited practical value; in planning the dose, the analysis of the specific batch should be relied on, especially its fatty acid and water content.

Methodology in brief

BMP is the amount of methane obtained from volatile solids (VS) in a batch test, given in m³ CH₄ per tonne of VS (numerically the same as NmL CH₄/g VS in the publications) and converted to normal conditions (0 °C, 101.325 kPa). The weighted mean gives each publication a total weight of 1, split equally between its results for the substrate — a paper testing twenty varieties does not outweigh a paper with a single sample. In inter-laboratory programmes the unit is the laboratory (total weight 1), and within it the weight of a test grows with the number of bottles (replicates). Results after pretreatment (e.g. thermal, chemical, enzymatic) are shown separately and are not included in the mean.

Solid lines are curves measured in the tests. Where a publication gives only the final result, we draw a first-order kinetic model, B(t) = B₀·(1 − e^−kt): only the end point comes from the publication, and the shape of the curve serves purely as visualisation — do not read the production on a particular day from it. For this substrate k = 0.091 d⁻¹ was assumed (no kinetic data for the group – the median of all available rate constants k (93 values) was used).

The statistics describe the spread of published results — a descriptive compilation, not a meta-analysis or a guarantee of plant yield.

Full methodology and correction policy

Bibliography

All sources of the site: bibliography.